>those are just colors. what about font type/size or padding, or background image et cetera?
There are variables for font family and font sizes (even sum presets I made, e.g. one for serif text, one for MS PGothic-style text, etc.), but you can still style other things the usual way. Even then, it should be easier since:

- All layout/structural CSS (base.css) has been separated from the theme-specific CSS (futaba.css, tomorrow.css, etc.)
- Duplicate CSS across multiple files has been removed
- Styling that was previously done with HTML elements and/or deprecated attributes has largely been replaced with proper IDs/classes + CSS
- Inline CSS (style="") and CSS injected by JS files has been removed/reduced

This means that new/custom stylesheets can be extremely small and simple, and very easy to maek. Pic related is the entirety of fuuka.css for overhaul ヽ(´ー｀)ノ